The present embodiments relate to a motor equipped with a transmission.
The power P of a motor may be described using P=M*ω, where M denotes the torque of the motor and w=2*πn denotes the angular speed at a rotational speed n of the motor. The power P may thus evidently be provided by a high torque M and/or a high rotational speed n.
Low-rotational-speed direct drives (e.g., drives that are operated at a low rotational speed n and are coupled directly to the component to be driven) exhibit a high torque and are operated at the same rotational speed as the component to be driven. These drives therefore have the advantage that the drives operate without an additional transmission. Owing to the demand for a high torque, these motors are, however, normally very heavy.
By contrast, in the case of high-rotational-speed motors, there is the advantage that a torque, which is indirectly proportional to the rotational speed, is sufficient for imparting the same power. In other words, the higher the rotational speed is selected to be, the lower is the torque required for imparting the same power. Since the torque is scaled with a factor that is dependent on the air gap diameter of the motor and the active length thereof (e.g., on the dimensions or on the size of the motor) and, as mentioned, in the case of high-rotational-speed motors, lower torques are sufficient for imparting the same power, it is possible for high-rotational-speed motors to be of relatively small construction, and the high-rotational-speed motors correspondingly take up less structural space and have a smaller mass.
In the case of these high-rotational-speed motors, there is, however, the disadvantage that these high rotational speeds are to be reduced again to the actually usable rotational speed by a corresponding transmission. Such a transmission is typically made up of a multiplicity of components (e.g., gearwheels, components for cooling, housing, screws, bearings, etc.). For this reason, the use of a transmission of the type consequently results in a significant additional mass. The actual mass advantage of the high-rotational-speed motor in relation to the direct drive may be lost again owing to the transmission that is possibly required and the associated additional mass.
A further difficulty of the high-rotational-speed motor lies in the fact that, in certain applications (e.g., in the case of wheel hub motors or propeller drives), it would be advantageous if the output side were situated at the outside, as in the case of an external-rotor motor. For example, in the case of high-rotational-speed motors, however, owing to the centrifugal forces that arise during rotational movements, there are limitations with regard to the practicable outer diameter of the rotating shaft and of the rotor. Thus, in these applications with an external rotor, it is necessary to forgo the weight advantage of the high-rotational-speed motor and adopt the heavier design of the external-rotor motor as a direct drive. It would alternatively be necessary, in this case, too, to use a transmission in combination with the high-rotational-speed motor, which, however, introduces an additional mass.
A transmission is typically mostly available as a separate component that is coupled to the motor by corresponding connections, attachments, and fits. As already indicated above, the various transmission components give rise to additional mass. A transmission generally has a flange or the like to which the unit to be driven, such as, for example, a propeller or a wheel, is coupled. The flange itself and the components associated therewith, such as, for example, bearings, various screws, housing, etc., in turn contribute, with corresponding masses, to the overall mass of the drive system, which ultimately has an adverse effect on the attainable power density.